It really depends on the person. Out of everyone I know I would say it's split about 50/50 on which was their first invert. Since they are done totally differently it probably just depends on what you're good at to begin with. Tantrum = start wide, flatten off and is a trip flip invert. Backroll = much shorter cut, very progressive up and through the wake. Factoring in whether you're more comfortable with backflips or front flips also helps.